Palladium-catalyzed novel arylations of cyclic β-bromo α,β-unsaturated aldehydes with triarylbismuths as multicoupling organometallic nucleo-philes

Article abstract of DOI:10.1055/s-0030-1259290

Cross-coupling arylations of cyclic β-bromo α,β -unsaturated aldehydes were carried out with triarylbismuths as atom-efficient multicoupling organometallic reagents under palladium-catalyzed conditions. These reactions afforded the corresponding arylated alkenes in an efficient manner with good to high yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0030-1259290

LETTER
273
Palladium-Catalyzed Novel Arylations of Cyclic b-Bromo a,b-Unsaturated
Aldehydes with Triarylbismuths as Multicoupling Organometallic Nucleo-
philes
C
ross-Coupling Arylat
a
ions of Cyc
d
lic
b
-Bromo
d
a
,
b
-Unsatu
a
rate
d
A
ldeh
l
yde
s
i L. N. Rao,* Debasis Banerjee, Ritesh J. Dhanorkar
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
Fax +91(512)2597532; E-mail: maddali@iitk.ac.in
Received 13 August 2010
required for the coupling studies was prepared from a-te-
tralone following the literature procedure.5h The investi-
gation was carried out using 1-bromo-3,4-
dihydronaphthalene-2-carbaldehyde (1a) with triphenyl-
bismuth (1b) under different conditions to obtain 1-phe-
nyl-3,4-dihydronaphthalene-2-carbaldehyde (2a) and
these results are summarized in Table 1.
Abstract: Cross-coupling arylations of cyclic b-bromo a,b -unsat-
urated aldehydes were carried out with triarylbismuths as atom-
efficient multicoupling organometallic reagents under palladium-
catalyzed conditions. These reactions afforded the corresponding
arylated alkenes in an efficient manner with good to high yields.
Key words: palladium catalysis, cyclic b-bromo a,b -unsaturated
aldehyde, cross-coupling, triarylbismuths, tetrasubstituted alkenes
Table 1 Screening Conditionsa,b
Ph
Br
Palladium-catalyzed coupling reactions are often em-
ployed in the synthesis of complex molecular systems.1 In
particular, regio- and stereoselective synthesis of tetrasub-
stituted alkenes is an important aspect in organic synthe-
sis. There is a constant demand for new strategies for the
synthesis of these systems. Tetrasubstituted olefins are
useful precursors in the synthesis of a variety of natural
products.2 These structures are also used for the synthesis
of molecular structures such as phenanthrene3 and quino-
line derivatives4 involving palladium-mediated Ullmann
cross-couplings.
CHO
CHO
+
[Pd]
BiPh3
Ph-Ph +
1b
1c
2a
1a
Entry Catalyst, base, solvent, temperature
1a 1c 2ac,d
1
2
PdCl2(PPh3)2, K2CO3, DMF, 90 °C
PdCl2(PPh3)2, Na2CO3, DMF, 90 °C
PdCl2(PPh3)2, Cs2CO3, DMF, 90 °C
PdCl2(PPh3)2, K3PO4, DMF, 90 °C
PdCl2(PPh3)2, K3PO4, NMP, 90 °C
PdCl2(PPh3)2, K3PO4, DMA, 90 °C
5
15
8
8
5
6
2
3
83 (75)
73 (65)
80 (70)
93 (96)
88 (80)
3
Similarly, b-halo a,b-unsaturated aldehydes represent an
important class of compounds in organic synthesis. These
compounds are useful in cycloaddition reactions of ene-
diyne and ene-allene functionalities.5,6 However, these
substrates have not been much investigated in coupling
reactions with organometallic reagents under metal catal-
ysis.3 We envisaged that such coupling with triaryl-
bismuths under palladium-catalyzed conditions would
provide a unique opportunity for chemoselective vinylic
arylations leading to synthetically useful molecular scaf-
folds under facile reaction conditions. The advantage as-
sociated with triarylbismuth compounds is that they serve
as atom-efficient multicoupling organometallic nucleo-
philes in reactions with three equivalents of an organic
electrophile.7 We have therefore studied the coupling re-
actions of cyclic b-bromo a,b-unsaturated cyclic alde-
hydes with triarylbismuths under palladium-catalyzed
conditions and the results are described herein.
4
2
5
3
6
3
16 81 (80)
7
PdCl2(PPh3)2, K3PO4, 1,4-dioxane, 90 °C 51
5
7
5
0
3
30 (21)
26 (17)
80 (75)e
42 (33)
0
8
PdCl2(PPh3)2, K3PO4, DMF, 25 °C
PdCl2(PPh3)2, K3PO4, DMF, 90 °C
PdCl2(PPh3)2, no base, DMF, 90 °C
no catalyst, K3PO4, DMF, 90 °C
44
11
32
72
9
10
11
a Conditions: BiPh3 (1 equiv, 0.25 mmol), 1-bromo-3,4-dihydronaph-
thalene-2-carbaldehyde (3.3 equiv, 0.825 mmol), base (2 equiv),
PdCl2(PPh3)2 (0.09 equiv, 0.0225 mmol), solvent (3 mL), 1 h.
b GC conversions of the crude reaction mixture.
c Isolated yields are given in parenthesis.
d Yields are calculated with respect to 3 equiv of cross-coupling prod-
uct (0.75 mmol) as 100% yield.
e The reaction was carried out with 1 equiv of K3PO4 base.
The coupling reactivity of b-bromo a,b-unsaturated cyclic
aldehydes with triarylbismuths was studied through sys-
tematic screening under palladium-catalyzed conditions.
The 1-bromo-3,4-dihydronaphthalene-2-carbaldehyde (1a)
The initial screening of PdCl2(PPh3)2 as catalyst with a set
of different bases was studied to check their efficacy in
N,N-dimethylformamide (DMF) to give the product 2a
(Table 1, entries 1–4). From this study, K3PO4 base was
found to be a better choice in comparison with other bases
SYNLETT 2011, No. 2, pp 0273–0279
x
x.
x
x.
2
0
1
1
Advanced online publication: 23.12.2010
DOI: 10.1055/s-0030-1259290; Art ID: D22110ST
© Georg Thieme Verlag Stuttgart · New York

274
M. L. N. Rao et al.
LETTER
studied (Table 1, entry 4), although it should be noted that give three equivalents of cross-coupling product 2a and
bases such as K2CO3, Na2CO3 and Cs2CO3 also furnished these couplings were completed in a short reaction time.
the product 2a in reasonably good yields. Further study
This encouraged us to extend the study to assess the scope
was carried out in different solvents (Table 1, entries 5–
of these couplings using PdCl2(PPh3)2 (0.09 equiv),
7). This study revealed DMF as the better solvent among
K3PO4 base (2 equiv) in DMF solvent at 90 °C, for one
other polar aprotic solvents studied such as N-methyl-2-
hour as the optimized conditions.9,10 As shown in Table 2,
the cross-coupling reactions of a variety of functionalized
triarylbismuths were studied with both 1-bromo-3,4-dihy-
pyrrolidone (NMP) and N,N-dimethylacetamide, while
1,4-dioxane was found to be less effective. A coupling
reaction carried out under room temperature condition
dronaphthalene-2-carbaldehyde and 1-bromo-3,4-dihy-
provided lower product conversion (Table 1, entry 8).
dro-6-methoxynaphthalene-2-carbaldehyde compounds.
Further study with one equivalent of base produced 75%
Regardless of the nature of triarylbismuths employed, the
of coupled product (Table 1, entry 9). A control reaction
reactions afforded good to excellent yields of cross-cou-
without base furnished the cross-coupling product in low-
pled products. For example, electronically divergent tri-
er yield (Table 1, entry 10), while reaction without cata-
arylbismuths with both electron-rich and electron-
lyst failed to provide the desired cross-coupling product
deficient aryl groups fared well under the established pal-
(Table 1, entry 11). As shown in the Table 1, the reaction
ladium protocol condition (Table 2, entries 1–17). It
also produced homocoupled biphenyl as a side product in
should be highlighted that three equivalents of either 1-
varied amounts under the conditions studied. This is due
bromo-3,4-dihydronaphthalene-2-carbaldehyde or 1-bro-
to the facile homocoupling reactivity of triarylbismuths
mo-3,4-dihydro-6-methoxynaphthalene-2-carbaldehyde
reacted very efficiently with one equivalent of triarylbis-
muth in a short time. We also examined the cross-
coupling reaction using tris(thiophenyl-2-yl)bismuth and
this afforded the corresponding product in high yield
(Table 2, entry 18). Additionally, the sterically bulky
tris(2-naphthyl)bismuth provided the corresponding cou-
pled product in 89% yield (Table 2, entry 19).
under the palladium-catalyzed conditions.8 Unreacted
bromide was also seen in these screening reactions and the
amount varied with respect to formation of the cross-cou-
pling product. Finally it emerged that PdCl2(PPh3)2 with
K3PO4 base in DMF solvent was the most suitable combi-
nation to obtain product 2a in 96% isolated yield in one
hour reaction time (Table 1, entry 4). It is noteworthy that
the overall process involves three couplings from triphe-
nylbismuth with three equivalents of bromoaldehyde to
Table 2 Cross-Couplings with Different Triarylbismuth Compoundsa–d
R1
Br
CHO
CHO
PdCl2(PPh3)2 (0.09 equiv)
Bi
+
K3PO4 (2 equiv)
DMF, 90 °C, 1h
3
R2
R1
R2
(1 equiv)
(3 equiv)
(3 equiv)
Entry
BiAr3
Bromoaldehyde
Product
Yield (%)
Br
1
2
R2 = H
2a
3a
96
80
CHO
Bi
R2 = OMe
CHO
3
R2
R2
3
4
R2 = H
2b
3b
83
86
Bi
R2 = OMe
CHO
3
R2
Br
CHO
5
2c
85
Bi
CHO
3
Synlett 2011, No. 2, 273–279 © Thieme Stuttgart · New York

LETTER
Cross-Coupling Arylations of Cyclic b-Bromo a,b -Unsaturated Aldehydes
275
Table 2 Cross-Couplings with Different Triarylbismuth Compoundsa–d (continued)
R1
CHO
Br
CHO
PdCl2(PPh3)2 (0.09 equiv)
Bi
+
K3PO4 (2 equiv)
DMF, 90 °C, 1h
3
R2
R1
R2
(1 equiv)
(3 equiv)
(3 equiv)
Entry
BiAr3
Bromoaldehyde
Product
Yield (%)
OMe
Br
6
7
R2 = H
2d
3c
76
86
CHO
OMe
Bi
R2 = OMe
3
CHO
R2
R2
OMe
OMe
Br
CHO
8
2e
85
Bi
CHO
3
OEt
Br
9
10
R2 = H
2f
3d
86
86
CHO
OEt
Bi
R2 = OMe
3
CHO
CHO
CHO
CHO
R2
R2
R2
R2
R2
Oi-Pr
11
12
R2 = H
2g
3e
95
85
Oi-Pr
Bi
R2 = OMe
3
Cl
13
14
R2 = H
2h
3f
83
76
Cl
Bi
R2 = OMe
3
F
15
16
R2 = H
2i
3g
89
85
F
R2 = OMe
Bi
3
CF3
CF3
Br
CHO
17
2j
68
Bi
CHO
3
Synlett 2011, No. 2, 273–279 © Thieme Stuttgart · New York

276
M. L. N. Rao et al.
LETTER
Table 2 Cross-Couplings with Different Triarylbismuth Compoundsa–d (continued)
R1
CHO
Br
CHO
PdCl2(PPh3)2 (0.09 equiv)
Bi
+
K3PO4 (2 equiv)
DMF, 90 °C, 1h
3
R2
R1
R2
(1 equiv)
(3 equiv)
(3 equiv)
Entry
BiAr3
Bromoaldehyde
Product
Yield (%)
75
S
S
18
19
2k
2l
CHO
Bi
Bi
3
89
CHO
a Reaction conditions: BiAr3 (0.25 mmol, 1 equiv), bromoaldehyde (0.825 mmol, 3.3 equiv), K3PO4 (0.5 mmol, 2 equiv), PdCl2(PPh3)2 (0.0225
mmol, 0.09 equiv), DMF (3 mL), 90 °C, 1 h.
b Isolated yields are based on three couplings, i.e. 3 equiv of cross-coupling product (0.75 mmol) as 100% yield.
c Biaryl as homocoupled products were formed in minor amounts.
d All products were characterized by 1H NMR, 13C NMR, HRMS (ESI) and IR analyses.
Next we turned our attention to investigate the reactivity ate B (Scheme 1). This, upon transmetalation with BiAr
of b-bromo-a,b-cycloalkenyl aldehydes with triarylbis- species would form the intermediate C. This is expected
muths.9,10 As shown in Table 3, these bromoaldehydes to undergo a facile reductive elimination to deliver the
also led to moderate to good yields of the coupled prod- arylated product D. As the reaction involves transfer of
ucts. For example, reaction using (Z)-2-bromocyclo-1- three aryl groups during the reaction cycle, the possibility
octenecarbaldehyde furnished a moderate yield of the of aryl transfer from BiAr3, Ar2BiX or ArBiX2 is not ruled
coupling product (Table 3, entry 1). Both 2-bromo-5-tert- out.
butylcyclohex-1-enecarbaldehyde and 2-bromocyclo-
pent-1-enecarbaldehyde reacted well in coupling reac-
X
Ar
tions with a variety of triarylbismuth compounds under
the established conditions (Table 3, entries 2–12). Once
again, all the reactions furnished the corresponding cross-
coupling products in a short reaction time.
Pd(0)
R
R
A
D
X = Br
oxidative
addition
R = CHO
reductive
elimination
Coupling products such as the 1-aryl-3,4-dihydronaphtha-
lene derivatives are important intermediates in the synthe-
sis of biologically active compounds,11,12 useful as oral
anti-fertility agents, in the treatment of diabetic complica-
tions and in combating HIV infections.
Pd(II)X
Pd(II)Ar
R
R
C
B
transmetalation
The cross-coupling of b-bromo a,b-unsaturated aldehydes
with triarylbismuths is expected to follow a reaction path-
way similar to that proposed by Stille et al. for the cou-
pling reactions of vinylic substrates under palladium-
catalyzed conditions.13 It is well established that the oxi-
dative addition of organic halides to zero-valent palladi-
um catalyst is a facile process.13a Based on this, it is
proposed that the initial oxidative addition of vinyl halide
to palladium(0) forms the organopalladium(II) intermedi-
Bi-Ar
Bi-X
Scheme 1 Proposed catalytic cycle
The regeneration of BiAr3 from the disproportion reaction
of arylbismuth halides generated in situ during the reac-
tion could be another possibility for aryl transfer in the
transmetalation step.8
Synlett 2011, No. 2, 273–279 © Thieme Stuttgart · New York

LETTER
Cross-Coupling Arylations of Cyclic b-Bromo a,b -Unsaturated Aldehydes
277
Table 3 Arylations of b-Bromoalkenyl-1-carbaldehydesa–d
R2
Br
PdCl2(PPh3)2
R1
(0.09 equiv)
Bi
+
R1
K3PO4 (2 equiv)
DMF, 90 °C, 1 h
CHO
R2
CHO
(3 equiv)
3
(3 equiv)
(1 equiv)
Entry
Bromoaldehyde
BiAr3
Product
Yield (%)
63
Br
Bi
1
CHO
3
CHO
4a
Br
2
61
Bi
CHO
CHO
3
5a
3
4
5
65
89
70
Bi
3
CHO
CHO
CHO
CHO
CHO
CHO
5b
5c
Bi
Bi
3
OMe
OEt
Oi-Pr
Cl
OMe
3
5d
5e
5f
6
7
8
75
67
61
Bi
OEt
3
Oi-Pr
Bi
Bi
3
Cl
3
5g
Synlett 2011, No. 2, 273–279 © Thieme Stuttgart · New York

278
M. L. N. Rao et al.
LETTER
Table 3 Arylations of b-Bromoalkenyl-1-carbaldehydesa–d (continued)
R2
Br
PdCl2(PPh3)2
R1
(0.09 equiv)
Bi
+
R1
K3PO4 (2 equiv)
DMF, 90 °C, 1 h
CHO
R2
CHO
(3 equiv)
3
(3 equiv)
(1 equiv)
Entry
Bromoaldehyde
BiAr3
Product
Yield (%)
F
9
67
Bi
F
3
CHO
5h
6a
6b
6c
OMe
Br
10
11
12
77
75
76
Bi
Bi
Bi
OMe
OEt
3
CHO
CHO
CHO
CHO
OEt
3
Oi-Pr
Oi-Pr
3
a Reaction conditions: BiAr3 (0.25 mmol, 1 equiv), bromoaldehyde (0.825 mmol, 3.3 equiv), K3PO4 (0.5 mmol, 2 equiv), PdCl2(PPh3)2 (0.0225
mmol, 0.09 equiv), DMF (3 mL), 90 °C, 1 h.
b Isolated yields are based on three couplings i.e. 3 equiv of cross-coupling product (0.75 mmol) as 100% yield.
c Biaryl as homocoupled products were formed in minor amounts.
d All products were characterized by 1H NMR, 13C NMR, HRMS (ESI) and IR analyses.
In conclusion a novel coupling method is described for the
synthesis of functionalized cyclic tetrasubstituted olefin
derivatives. This efficient protocol uses triarylbismuths as
atom-efficient multicoupling nucleophiles with three
equivalents of cyclic b-bromo a,b-unsaturated aldehydes
in a synthetically versatile and a useful method under pal-
ladium-catalyzed conditions. The multicoupling ability of
triarylbismuths has been demonstrated to be facile, as all
coupling reactions were complete within one hour giving
high yields of coupling products.
References and Notes
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(9) Representative Procedure: An oven-dried Schlenk tube
under a nitrogen atmosphere was charged with 1-bromo-3,4-
dihydronaphthalene-2-carbaldehyde (0.825 mmol, 0.196 g)
followed by triphenylbismuth (0.25 mmol, 0.11 g), K3PO4
(0.50 mmol, 0.106 g), PdCl2(PPh3)2 (0.0225 mmol, 0.0158
g) and anhyd DMF (3 mL). The reaction mixture was stirred
in an oil bath at 90 °C for 1 h. Then the contents were cooled
to r.t. and the reaction was quenched with H2O (10 mL) and
the mixture was extracted with EtOAc (3 × 15 mL). The
combined organic extracts were washed with H2O (2 × 10
mL), brine (10 mL), dried over anhyd MgSO4 and
concentrated. The crude product mixture thus obtained was
purified by silica gel column chromatography using 1%
EtOAc–petroleum ether as eluent to obtain 1-phenyl-3,4-
dihydronaphthale-2-carbaldehyde(2a) as a pale yellow solid
(0.169 g, 96%). All the products were characterized by 1H
NMR, 13C NMR, IR spectroscopic data and HRMS (ESI).
(10) In all the coupling reactions, 0.3 equiv of bromoaldehydes
was employed in excess. However, the product yields were
calculated based on the three couplings from triaryl-
bismuths. Thus, 0.75 mmol of the cross-coupled product
corresponds to 100% yield.
(11) Moleele, S. S.; Michael, J. P.; de Koning, C. B. Tetrahedron
2006, 62, 2831.
(12) Shagufta; Raghunandan, R.; Maulik, P. R.; Panda, G.
Tetrahedron Lett. 2005, 46, 5337.
(13) For mechanistic, see: (a) Scott, W. J.; Stille, J. K. J. Am.
Chem. Soc. 1986, 108, 3033. (b) Jutand, A.; Mosleh, A.
Organometallics 1995, 14, 1810. (c) Jutand, A.; Négri, S.
Organometallics 2003, 22, 4229.
Synlett 2011, No. 2, 273–279 © Thieme Stuttgart · New York

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